Short description
(French)
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Ce projet vise à l'amélioration du rendement externe des diodes électroluminescentes à base de nitrures d'éléments III en vue de leur application à l'éclairage. Dans ce cadre, nous privilégierons trois grands axes de recherche à savoir les effets de microcavités, l'utilisation de boîtes quantiques dans la zone active, et la croissance sur de nouveaux substrats.
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Partners and International Organizations
(English)
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AT, BE, BG, HR, CZ, FI, FR, DE, EL, HU, IT, LV, LT, NL, PT, RO, ES, SE, CH, UK
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Abstract
(English)
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The main objective of this project is to investigate new routes for the improvement of the radiative efficiency of green light emitting diodes (LEDs) based on group-III nitride compounds. With the aim of solid-state lighting, green LEDs combined with blue and red ones present a promizing alternative to monolithic white LEDs based on phosphors pumped by blue or UV LEDs. Up to now, device-quality nitride epilayers have been mainly developed on c-plane sapphire substrates for which the growing plane is perpendicular to the (0001) polar axis. This epitaxial orientation conjugated to the crystal symetry of wurtzite nitride compounds has a detrimental consequence on the radiative efficiency of quantum wells, which are the active building block in LEDs. Actually, a giant electric field builds in the QWs and induces a separation of the electrons and holes, decreasing thereby the photon emission probability. This is especially the case for long-wavelength emitting GaN based LEDs (from green to red). Interestingly, the internal electric field can be suppressed if the QW interface planes are parallel to the (0001) GaN polar axis. This condition can be fulfilled using r-plane sapphire substrates thanks to appropriate epitaxial relationship. However, the quality of GaN layers deposited on such substrates is pocompared to that currently achieved on c-plane sapphire substrates. Thus the present project aims at i) improving the growth of GaN layers on r-plane sapphire substrates and ii) fabricating green LEDs from these layers. Two different growth techniques, metal-organics vapor phase epitaxy and hydride vapor phase epitaxy, have been considered. Epitaxial lateral overgrowth (ELO) process is also carried out to reduce the defect density.
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